Fibre Channel (FC) is a known networking protocol for high speed communications. Ethernet is another known networking protocol. As Ethernet networks have become faster and more capable another known protocol—Fibre Channel over Ethernet (FCoE) has emerged. FCoE is intended to allow FC-like communication over Ethernet networks by tunneling FC frames over Ethernet. Due to their high speed and reliability FC and FCoE are often used for storage area networks (SANs).
Both Fibre Channel and Ethernet use frames for communication. Frames are sets of data that are sequentially transmitted that include one or more header and/or trailer fields indicating various transmission related information (such as sender and recipient identification, etc.) and a data or payload field including the data that is actually being transmitted by the frame. Fibre Channel allows for variable size frames, but currently limits the data field of its frames to a maximum of 2112 bytes. This limit is also preserved in the FCoE standard. However, the Ethernet standard currently allows for larger frames, e.g., ones with frame length of up to 9000 bytes (some implementations of Ethernet that are not strictly standard compliant may allow for frames with frame length of up to 12000 bytes).
Since FCoE is often used for storage networking and thus for communications with storage devices, various sets of data that need to be transferred over FCoE are often significantly larger than the 2112 byte limit to the data field of an FCoE frame. Therefore, often multiple FCoE frames may need to be transmitted to perform a requested data transfer (e.g. a hard drive write or read operation). The use of large number of frames tends to increase latency and/or the computational requirements at the devices that transmit the frames, those that receive the frames as well as intermediary devices that forward the frames over a network. Sender devices must split data to be sent into multiple payloads for multiple frames, construct each frame and place the proper headers in it. Receiver devices must process the headers of each received frame and recombine the multiple payloads of received frames in a single data set. Intermediary devices (such as switches and routers) may need to examine the headers of each received frame to determine where to forward it to.
When to end devices set up a communication link over FC or FCoE (as well as other protocols, such as Ethernet), they usually negotiate a maximum frame size for the communications link. The maximum frame size must be such that it can be handled by both end devices, as well as any networking devices (e.g., hubs, switches, routers, etc.) which are to transport the communications between the two end devices over the network. The maximum frame size is referred to as a maximum transfer unit (MTU). The process of negotiating the maximum frame size is referred to as “path MTU discovery” as it involves discovering the MTU for the entire path of communication between the end devices. There exist path MTU discovery protocols for existing FC and FCoE protocols, however these protocols are limited to frames with maximum payload of 2112 bytes and cannot negotiate larger frames.